Blood pumps are indispensable for conducting extracorporeal blood circulation in an artificial heart and lung apparatus and the like. A turbo type blood pump is known as one of the blood pumps. The turbo type blood pump rotates an impeller in a pump chamber having inlet and outlet ports to generate a differential pressure for sending blood with a centrifugal force.
The turbo type blood pump enables a blood pump to be miniaturized and reduced in weight and cost. Furthermore, the turbo type blood pump is excellent in durability since it is not affected by a tube damage or the like unlike a roller-pump type blood pump; therefore, the turbo type blood pump can be used preferably for continuous operation for a long period of time. Thus, the turbo type blood pump is becoming mainstream as a blood pump for an extracorporeal circulation circuit in an artificial heart and lung apparatus or a cardioassist apparatus after open-heart surgery.
In an exemplary turbo type blood pump described in, for example, Patent Document 1, an impeller has a configuration in which a plurality of vanes are provided radially on a circular conical surface of a conical base. The bottom surface of the base has an area to such a degree as to cover almost the entire bottom surface of a housing, so that a whirlpool does not occur in the vicinity of the base, and hence, there is no problem of hemolysis caused by the whirlpool.
However, a stagnant portion of blood is formed in a gap that is present necessarily between the lower surface of the base and the housing, and the heat generated in the bearing portion of the impeller is accumulated in the stagnant blood. Then, due to the influence of the heat in the stagnant portion combined with the shear force caused by the rotation of the impeller, there arises a problem that hemolysis occurs in the stagnant portion. In order to solve this problem, according to Patent Document 1, a blood circulation hole extending from the upper surface to the lower surface is provided in the base. The blood circulation hole allows the blood in the stagnant portion to pass through the vicinity of the bearing portion to reach the upper surface of the base through the blood circulation hole and to flow toward an outer diameter direction of the vanes smoothly, whereby the effect of preventing stagnation can be obtained.
On the other hand, the turbo type blood pump of Patent Document 1 uses a configuration in which the drive force of the impeller is provided from outside via a housing wall through magnetic coupling. More specifically, a magnet is attached to the lower portion of the conical base of the impeller, and a magnet for driving is placed below the outside of the housing so as to be opposed to the magnet of the impeller. The magnet for driving is rotated by a motor, and the impeller is rotated via the magnet of the impeller through magnetic coupling.
However, the configuration for supporting the impeller rotatably, i.e., the bearing structure is provided only in a lower end portion of the impeller. Furthermore, the bottom surface of the conical base has a size so as to cover almost the entire bottom surface of the housing, so that the drive force provided from outside for rotating the impeller becomes large. Consequently, when an attractive force caused by magnetic coupling for providing a drive force is exerted, the supported state of the impeller is likely to be unstable due to the support structure only in the lower end portion.
In order to solve the problem, the turbo type blood pump described in Patent Document 2 has a horizontal cross-sectional configuration as shown in FIG. 6. In FIG. 6, reference numeral 1 denotes a housing, in which a pump chamber 2 for passing and flowing blood is formed, and an inlet port 3 communicated with the upper portion of the pump chamber 2 and an outlet port 4 communicated with the side portion of the pump chamber 2 are provided. An impeller 5 is placed in the pump chamber 2. FIG. 7 shows a top view of the impeller 5. The impeller 5 includes six vanes 6, a rotating shaft 7, and a ring-shaped annular coupling portion 8.
As shown in FIG. 7, the six vanes 6 include 2 kinds of shapes: large vanes 6a and small vanes 6b, which are placed alternately. A center-side end portion of the large vane 6a is coupled to the rotating shaft 7 via an arm 18, and a circumferential side end portion thereof is connected the annular connecting portion 8. A center-side end portion of the small vane 6b is a free end not coupled to the rotating shaft 7, and only each circumferential end portion thereof is coupled to the annular coupling portion 8. This is because the number of the arms 18 increases when all the vanes 6 are coupled to the rotating shaft 7, interfering with a flow path, which is not preferred. A minimum number of the arms 18 required for transmitting the rotation of the impeller to the rotating shaft 7 may be provided. As is understood from the figure, the impeller 5 has a space 19 in a region inside the annular coupling portion 8, whereby a flow path passing vertically through the vanes 6 is formed.
As shown in FIG. 6, the rotating shaft 7 is supported rotatably by an upper bearing 9 and a lower bearing 10 provided at the housing 1. The annular coupling portion 8 is provided with a magnet case 11, where driven magnets 12 are buried and fixed. The driven magnets 12 have a cylindrical shape, and the six driven magnets 12 are placed at a predetermined interval in the circumferential direction of the annular coupling portion 8. The annular coupling portion 8 and the magnet case 11 form a cylindrical inner circumferential surface.
A rotor 13 is placed below the housing 1. The rotor 13 includes a drive shaft 14 and a substantially cylindrical magnetic coupling portion 15, which are coupled to each other. Although not shown, the drive shaft 14 is supported rotatably, and is coupled to a rotation drive source such as a motor to be rotated. Furthermore, although not shown, the relative positional relationship is kept constant between the rotor 13 and the housing 1. Drive magnets 16 are buried and fixed in an upper surface portion of the magnetic coupling portion 15. The drive magnets 16 have a cylindrical shape, and the six drive magnets 16 are placed at a predetermined interval in a circumferential direction.
The drive magnets 16 are placed so as to be opposed to the driven magnets 12 with a wall of the housing 1 interposed therebetween. Thus, the rotor 13 and the impeller 5 are coupled to each other magnetically, and when the rotor 13 is rotated, the impeller 5 is rotated through magnetic coupling.
Abase 20 having a cylindrical outer circumferential surface, which protrudes upward, i.e., to the inside of the pump chamber 2, is formed at the center in a bottom portion of the housing 1. The base 20 is formed so as to fill the space 19 in a region inside the driven magnets 12 and the annular coupling portion 8 below the impeller 5, which minimizes the volume of the space. This reduces the filling amount of blood in the pump chamber 2.
The upper bearing 9 is placed at a position below the inlet port 3, penetrating the pump chamber 2. Three bearing pillars 17 are provided on the inner surface in a lower end portion of the inlet port 3, and extend diagonally downward to penetrate the pump chamber 2, and the upper bearing 9 is supported by the tip end of the bearing pillars 17 in the center portion of the flow path cross-section of the inlet port 3. The lower bearing 10 is provided at the center in an upper surface portion of the base 20.
In the turbo type blood pump with the above configuration, the impeller 5 is supported vertically by the upper bearing 9 and the lower bearing 10. Therefore, the supported state of the impeller 5 is stable, whereby the stable function of supplying blood can be obtained. Furthermore, the annular coupling portion 8 does not have a size covering the entire bottom surface of the housing 1 as in the conical base in Patent Document 1, and the impeller 5 has a space in a region spreading between the rotating shaft 7 and the annular coupling portion 8. Thus, the impeller 5 is light-weight, and a small drive force suffices.
Furthermore, a flow path passing through the vanes vertically is formed in the region spreading between the rotating shaft 7 and the annular coupling portion 8. Therefore, in the same way as in the function of the blood circulation hole in Patent Document 1, the blood in the stagnant portion formed in the lower portion of the impeller 5 passes through the vicinity of the lower bearing 10 to reach the upper portion of the impeller 5 and to flow toward the outer diameter direction of the impeller 5.    Patent Document 1: JP 4(1992)-224760 A    Patent Document 2: JP 2002-85554 A